Butt-seamed metal tube and method of making the same.



R. KOENIG. BUTT smmnn METAL TUBE AND METHOD OF MAKING THE SAME.

APPLICATION I'ILED JULY 27,1910.

l tentea Mar. 5, 1912.

" United States divided herefrom UNITED strATEs PATENT OFFICE.

ROBERT KOENIG, OF BROOKLYN, NEW YORK, ASSIGNOR TO PHENLX TUBE COMPANY,OF BROOKLYN, NEW YORK, A. CORPORATION OF NEW JERSEY.

.BUTT-SEAMED METAL TUBE ND METHOD or MAKING THE sAME.

To all whom it may concern.- I

Be it known that I, ROBERT KOENIG, a citizen of the United States, andresident of Brooklyn, in the co'untyof Kings and State of New York, haveinvented new and useful Improvements in Butt-Seamed Metal Tubes" andMethods of Making the Same, of which the following is a specification.

My invention relates to the construction of prismatic sheet metal tubes,and consists in a method of forming butt seamed tubes of sheet metal,and in the tube which is the product of-the said method.

The object which I have in view is to make prismatic metal tubingwhich,though simply formed with a butt seam, without welding or ofshapes, until the two edges of the strip meet, when the residualelasticity of the metal suffices to spring the edges of the seam apart.By my invention the operation of rolling and drawing the tube producesin it such internal strains that the normal condition at the seam is oneof mutual pressure between the meeting edges, so that the tube is andremains a closed tube.

T he essence of the method is the production' by rolling or drawing themetal, of longitudinally disposed narrow regions wherein the metal is ina condition of permanent internal strain, of which the resultant is abending moment which tends to alter the periphery of the tube as a wholeand therefore closes the seam tightly, and likewise, the characteristicwhich distinguishes my new product, is the presence in the structure ofa butt-seamed, sheet metal tube, of such longitudinally disposed narrowregions of internal stress I The mechanism by which the method isperformed and the structure produced, which mechanism forms the subjectmatter of an application for Letters Patent of the Serial No. 615,542,filed March 20, 1911, is characterized by an internal mandrel andexternal complementary die-members, which are all Specification ofLetters Patent.

so proportioned and disposed as to have internal and external clearancesat the places Patented Mar. 5, 1912. Application filed July 27, 1910.Serial No. 574,076.

where the'angles of the prismatic tube are formed, and to exert formingpressure on the sides of the prismatic tube so as to cause a flow of themetal of which the tube is composed, from each side outward toward theclearance-spaces wherein the angles of the tube are formed.

The structural condition presented by a butt-seamed, sheet metal tubehaving longitudinally disposed narrow regions of internal stress may be,and I believe is best, produced-by compressing the tube at intervalsaround its periphery, bet-ween the dies or rollers on the one hand, andan internal mandrel on the other, so that the metal flows slightly inboth directions out of the compressed regions, each local flow meetingan oppositely directed flow proceeding from an adjoining region ofcompression. meeting place of these two opposed flows of metal thusbecomes a region of internal strain which when the tube emerges from therestraint of ,the instruments which formed it, holds .the two edges ofthe seam tightly pressed together, producing an apparently seamlesstube, instead of the openderstood from a description of the method offorming a square tube, of the instruments used to carry out the method,and of the structure of the tube itself.

A concrete example of .my invention is illustrated in'the drawingshereto annexed, in which Figures 1 to 1 represent diagrammatically threepreliminary stages of the manufacture of a prismatic tube out of fiatsheet metal; Fig. 2 represents, partly in cross section, onalargerscale, the instrmnents for fornnn a s uaretube and the tube therein b 77 I projection or bur indicated at 6 along the cut edges on one side ofthe strip. For purposes presently to be explained, I so place the stripof metal in the bending machine that when the cylindrical tube isformed, the burs lie on the outside. The formation of the cylindricaltube involves a rolling and drawing in any of the well known machines'suited to the purpose, which first shapes the tube in channel formhaving a rounded U section as indicated in Fig. 1 and then further rollsand draws the metal so that the cylindrical tube shown in cross sectionin Fig. 1 is the result. The mandrel and die which give the finalcylindrical shape to the metal bring the two edges of the strip closetogether, but then the residual elasticity of the metal causes the twoedges of the seam to spring apart slightly leaving a gap such as shownat g in Fig. 1. The cylindrical, open-seam tube is then placed in themachine which is to convert it into a prismatic tube with a closed buttseam.

For purposes of illustration, I take the case of a square tube to bemade from the round tube above described. A drawbench machine such asused for squaring seamless drawn tubing, will serve my purpose, withchanges in the mandrel and roller dies, as hereinbelow described. Thetools or instruments in the machine for forming the square tube whichimmediately perform the work, consist of an internal mandrel marked M inFig. 2 and a roller die or former composed of four external rolls Rwhich are op posed to the sides of the mandrel. This mandrel is held inposition by a rod M which is laid in the cylindrical tube of metal andis anchored outside the end of the tube to a convenient portion of theframe of the drawing machine. The forward-end of the tube is gripped bythe traveling jaws of the drawing machine in the usual manner. Thearrangement of four 'rolls which constitute the external former or dieis in general the same as that shown in Figs. 1 and 2 of Carrs UnitedStates Patent No;.402,140, and the positional relationship of themandrel and sheet metal tube to each other and to the rolls is much thesame as that shown in Fig. 1 of Ostranders United States Patent No.113,332.

The mandrel M and rolls R operate upon all portions of themetal tubeexcept at and near thecorners of the prism which is formed by therolling and drawing operation. Thus the edges of the rolls R as shown inFig. 2 are well inside of the salient angles of the square tube and theedges of the mandrel M are chamfered OK at the corners at m, so that theactive pressure and drawing friction is exerted on the inside by thesides m of the mandrel M and on the outside by the rolls R.

The provision of clearance between the operating instruments at thecorners thereof or rather at the places where the salient angles oredges of the tube are formed, together with the heavy pressure broughtto bear between the mandrel and the rolls bends and compresses the metalof which the round tube was formed and which is being squared in themachine, at the sides of the squared tube and this causes a flow of themetal of which the tube is composed from the sides toward the angles,the direction of this flow being indicated by the'arrows in Fig. 2.Therefore at each corner C of the square tube the flow of metal comingfrom two directions produces a region which is set in compression ateach salient angle of the tube; these compression regions are indicatedconventionally by heavy shading at the points C in Fig. 2.

The dimensions of the mandrel M and rolls R are properly adapted to theperipheral dimensions of the round tube shown in section at Fig. 1, sothat in forming the prismatic tube the edges of the gap' 9 are broughttogether. But when the prismatic tube has been formed as abovedescribed, the presence at the salient angles of the tube of regions inwhich the metal of which the tube is formed is under internalcompressive strain produces a resultant of contractile effort ascontrasted with the residual expansive elasticity manifest in the roundtube shown in Fig. 1 and the edges of the seam at g' are held in closemutual abutment. As the burs b were left at the outside of the tube,these are rolled into the seam 9 so as to fill the slight irregularitiesdue to imperfect cutting of the strip in the first place.

Butt-seamed prismatic tubes formed as above described present to the eyethe appearance of seamless drawn tubes and are amply strong for manylight structural purposes, such as the manufacture of metal bedsteads orother furniture, and by reason of the simplicity of their method ofmanufacture, can be made more rapidlyand cheaply .What I claim anddesire to secure by .Let- 't"'t'S Patent is:

1. The method, of makin buttseamed tubes, which consists in hen ing asheet of s metal into tubular form and then producing in the sheet apermanent peripherally con-- tractile internal strain.

-2. The method of making butt-seamed tubes, which consists in bending 5;metal *aeet into prismatic tubular. form and'pro nucing in the metal ofthe sheet at the salient angles 'of the prism a permanent, internal,compressive strain. t

3. The method of making butt-seamed 15 prismatic metal tubes,- whichconsists in bend sing a strip of metal intothe desired tubular form, andcompressing the metal at the sides of the rismcausing internal flowtoward the salient angles sufiicient to produce at said angles acondition of permanent internal compressive strain.

4. A tube consisting of a sheet of metal bent in prismatic form withedges in one of the faces of the prism abutting under mu tual pressure.

5. A tube consisting of a bent sheet of metal in prismatic form withabutting edges on one of the faces of the prism, thematerial of whichthe sheet is composed being under permanent internal compressive strainatthe salient angles of the rism.

Signed by me at Broo yn Kings Co. New York this 20th day of July 1910. 4

ROBERT KOENIG.

Witnesses:

A. P, ALVORD, CHAS. A. FoLLn'r'r.

